1. Field of the Invention
The present invention relates generally to electronic packaging of semiconductor integrated circuits. More specifically, the present invention relates to electronic packaging of photo-sensing semiconductor devices having a patterned layer formed on a surface of its substrate for optimizing performance.
2. Related Art
Novel electronic packaging techniques for applications incorporating photo-sensors are disclosed in co-pending U.S. patent application Ser. Nos. 10/692,816, 60/507,100, 10/829,273, and 60/536,536, the disclosures of which are incorporated herein by reference. FIGS. 1–2B illustratively show schematic cross-sectional views of certain exemplary electronic packages realized by such techniques, fuller descriptions of which are contained in such co-pending applications.
The package illustrated in FIG. 1 is typically suited for general applications, while that shown in FIGS. 2A, B is particularly well-suited for cellular telephone camera module applications, where compact size remains invariably among paramount concerns.
In packages of the type shown, a photo sensor device defines a certain photo-sensing area—defined at a center portion of a top surface in the configurations illustrated. A substrate having sufficient transmittance to light within a certain wavelength range of interest is provided with the photo sensor device. The substrate may be formed, for example, of a glass material where the photo-sensor device is to sense light, within the visual range in wavelength. Electrical interconnection lines and one or more passivation layers are formed over a front surface of the substrate (bottom surface of the substrate in the configuration illustrated); and, flipchip interconnections are typically employed between the photo-sensor device and substrate. A sealing structure is also provided for protecting the side wall portion of the photo-sensor device and the photo-sensing area that it extends about. Other structures such as solder balls and decoupling capacitances are also typically provided in the resulting package using suitable means known in the art, but their detailed description is not necessary for a clear understanding of the present invention, and for that reason not included.
In the electronic package configuration illustrated in FIGS. 1 and 2A, B, the photo-sensing area of the photo-sensing die opposes the front surface of the substrate, which in the figures forms the bottom face of the substrate. The substrate's front surface thus corresponding to the photo-sensing die's photo-sensing area is kept free of any interconnection metal traces or passivation layer in order not to block or otherwise disturb the light entering the photo-sensing area through that portion of the substrate.
Light, however, may enter the photo-sensing area through other undesirable paths. Such structures as a patterned metal layer are formed on the substrate's front surface, at portions thereof outside the photo-sensing area. Given the transmittance of the substrate and the reflectivity of the patterned metal layer or other structure, light passing into the substrate at these outer portions may nonetheless enter the photo-sensing area itself by reflective paths. Even at those outer portions with non-metal structures, such as a passivation layer, their light transmittance properties may very well permit light to transmit through them to reach the photo-sensing die or other nearby surface to cause detrimental effect.
Light entering through such unintended peripheral paths are potentially disruptive to proper operation in several notable ways. For instance, edges of a patterned metal layer tend to reflect the impinging light in an irregular manner. Correspondingly irregular, and very complicated light transmission and reflection thereby result. Consequently, unwanted disturbances may be introduced into the light being sensed at the photo-sensing area. A need exists, therefore, to provide suitable protective measures for photo-sensing packages of various type by which such disturbances may be minimized or altogether eliminated.